LDMOS devices are finding increasing use in amplifier circuits--and, because of the high gain and linearity they exhibit, in power amplifier circuits, such as Class AB high power amplifiers. Testing as shown, however, that such LDMOS devices are very sensitive to bias voltages, to the extent that even as little as a 50 milli-volt change in the gate voltage could alter the drain current by as much as 30% or greater. For such reason, temperature compensation of these LDMOS devices has been found essential to offset the varying biasing voltages which follow from ambient temperature changes. This has been found particularly so with cellular telephone Base Station equipment at outside locations.
Testing has shown, though, that the typical method of providing temperature compensation of semiconductor amplifier devices leaves much to be desired. Analysis has revealed that this follows from the temperature compensation circuit's utilization of voltage dividers in which semiconductor diodes and/or thermistors are coupled across the input and control electrodes of the semiconductor device. Investigation has established that this results from the fact that the voltage source employed in such divider network is, itself, subject to temperature variation. For example, a nominal 5 volt supply has been determined to vary as much as 3% and more as temperatures rise, producing anywhere from a 0.5 to 1.0 millivolt per degree C. error. A fifty degree increase beyond room temperature could then produce a 50 millivolt increase in voltage, to such an extent as to significantly change the voltage divider bias on the LDMOS device, to drastically affect its performance, and because of its inherent gain and linearity. Thus, in these high power, LDMOS amplifier arrangements, something other than employing a voltage divider network for gate electrode temperature compensation is needed.